1. Field of the Invention
The present invention relates to a technique suitable for a photoelectric conversion device, and particularly an image sensing MOS photoelectric conversion device having a small pixel pitch.
2. Description of the Related Art
These days, CMOS sensors have been developed actively as image sensing devices using MOS transistors. The CMOS sensor uses a MOS transistor in a pixel to amplify a change of the potential caused by accumulated carriers photoelectrically converted by a photodiode. The CMOS sensor reads out video information as an electrical signal from each pixel to a peripheral region via a signal line. Japanese Patent Laid-Open No. 09-046596 discloses details of the CMOS sensor. Demands have recently arisen for higher-resolution, more compact video and digital cameras using image sensing devices, lower manufacturing cost, and lower power consumption. These demands boost the development of small-pixel CMOS sensors having a small pixel pitch.
The present inventors have studied reducing the pixels of CMOS sensors, and have found a problem different from one arising when reducing the pixels of CCD sensors. This problem is diffraction of light by a conductive line. The conductive line of a CMOS sensor is positioned on a transparent passivation insulating layer about several hundred nm to several μm thick on a semiconductor layer. Light is diffracted by the conductive line and diverges within an interlayer dielectric film before reaching the semiconductor layer. Part of the light enters an adjacent pixel.
A small-pixel CMOS sensor cannot completely collect light onto a photodiode owing to the diffraction limit of an on-chip microlens. If the conductive line overlaps the photodiode, it reflects a large part of light, decreasing sensitivity.